1. Field of the Invention
The present invention relates to a disk brake assembly for wheeled vehicles, and more particularly to a disk brake assembly includes a shim for preventing an uncomfortable squeak noise termed a "disk brake-echo". This is a phenomenon generated by the frictional contact between a brake pad and a caliper member, when the disk brake assembly is operated.
2. Description of the Prior Art
A disk brake assembly frequently generates what is termed a "disk brake-echo" phenomenon by a slip which occurs between the brake pad and the caliper member, when the disk brake assembly is operated. It is generally thought that the generation of the uncomfortable "disk brake-echo" phenomenon is caused by a minute vibration of the brake pad due to frictional engagement between the brake pad and the brake disk when the brake pad is pressed against the rotating brake disk. The vibration of the brake pad causes sympathetic vibrations of the brake disk or the caliper member. The sympathetic vibrations become an audio frequency which is then communicated with the occupant of wheeled vehicles as the squeak noise and make the occupant feel uncomfortable.
For preventing the uncomfortable squeak noise or "disk brake-echo" phenomenon, it has been proposed to provide a shim interposed between the caliper member and the brake pad in the prior art. A conventional disk brake of this kind is disclosed, for example, in U.S. Pat. No. 3,848,708, and Japanese Utility Model application laid-open publication No. 58-129,343 published on Sept. 1, 1983. These conventional disk brakes include having the shim interposed between the caliper member and the brake pad so as to absorb the vibration from the brake pad to caliper member. The shim consists of a steel plate and vibration-proof material covering the steel plate. The shim includes an engagement portion engaged with the brake pad so as to prevent slip of the shim with respect to the brake pad by relative displacement between the brake pad and the caliper member. The relative displacement is generated when the disk brake is operated. The shim includes an opening portion for exchanging the distribution of the surface pressure of the brake pad.
In the above conventional disk brake, however, the engagement portion is transformed by the relative displacement between the brake pad and the caliper member generated when the brake is operated under high load condition or under extended use of the disk brake. As a result, the engaging force of the engagement portion with respect to the brake pad falls and the shim slips with respect to the brake pad. Therefore, there is a drawback in the prior art that the assembly of the disk brake is damaged, since the caliper member or the piston only presses a part of the shim, the separation of the vibration-proof material is in a boundary portion between a pressed portion and an unpressed portion of the shim. Therefore, the durability of the shim is affected and, since the shim includes the opening portion, it is not possible to use the same shim on both of the left and right wheels.